This invention relates to a film forming unit that can form a metallic film or a metallic compound film by means of a low-pressure vapor-phase chemical reaction, for example that can deposit a metal for a circuit by means of a chemical vapor deposition process.
As a semiconductor device being an integrated circuit such as an IC is made more minute, a contact-hole for connecting different metallic-circuit layers to each other is also made more minute. That is, an aspect ratio (a ratio of a depth of the hole with respect to an open width) of the contact-hole is increased. In addition, there is known a method in which narrow grooves corresponding to a metallic-circuit pattern are formed in a surface of an insulating film in advance and then circuit elements are formed in the grooves (U.S. Pat. No. 4,789,648). In such a case, it is preferable that a metal for a circuit for forming the circuit element has a good coating characteristic and is deposited by a chemical vapor deposition method (CVD method) which is superior in an ability to fill a narrow groove.
The metallic film or the metallic compound film that is deposited by the CVD method may be W (tungsten), WSi, TiN, Ti, Al, Cu and so on. Herein, a film forming unit for W is explained as an example of a conventional film forming unit. FIG. 7 shows a schematic view of the film forming unit. The film forming unit has a processing container 2 which has a substantially cylindrical shape and in which a vacuum can be created. A stage 6 in which a heater 4 is buried is arranged in the processing container 2. A semiconductor wafer W as an object to be processed is adapted to be placed on the stage 6.
A circular clamping ring 8, which is connected to a pushing rod 10, is arranged around the stage 6 in a vertical movable manner. The inner side of the clamping ring 8 forms a taper (inclined) surface 8A that tapers upward. The taper surface 8A is adapted to come in contact with a circumferencial edge of the wafer W and to push down the same. Thus, the wafer W is adapted to be fixed on the stage 6.
A ceiling part opposite to the stage 6 has a showerhead 12 for supplying a process gas such as a film-forming gas into a processing space S in the processing container 2.
An inert-gas supplying nozzle 14 that introduces an inert gas such as Ar gas into a reverse-side space S1 of the stage 6 is provided below the stage 6, in order to prevent that the film-forming gas reaches a reverse side of the wafer W or a reverse side of the stage 6 and that any unnecessary film is deposited during the film-forming process.
During the film-forming process, the wafer W is maintained at a predetermined process temperature, and the film-forming gas is introduced from the showerhead 12 into the processing container 2. Then, the processing container 2 is evacuated to maintain a predetermined process pressure, so that a tungsten film or the like is deposited. At that time, an inert gas such as Ar gas is supplied from the inert-gas supplying nozzle 14 into the reverse-side space S1 on a reverse side of the stage 6. This prevents the film-forming gas from flowing into the reverse-side space S1 through a gap between the clamping ring 8 and the wafer. If an unnecessary film is deposited on a lateral or reverse surface of the wafer W, the unnecessary film may be pealed off to become particles during a subsequent process. In the case, the generation of particles is prevented.
FIG. 8 shows a partial sectional view of a semiconductor wafer in a condition wherein a film is formed ideally. In the condition shown in FIG. 8, a metallic film such as a tungsten film is deposited only on a surface (an upper surface in the drawing) of the wafer W, not on a lateral or reverse surface thereof.
Herein, the taper surface 8A of the clamping ring 8 comes in contact with the circumferencial edge of the wafer W in a linear contact manner. Thus, the contact state often may not become even i.e. may be uneven. The film-forming gas may flow into the reverse-side space S1 through a slight gap that is formed at the contact portion, so that an unnecessary film may be deposited on the lateral or reverse surface of the wafer W and on the stage 6. In addition, an unnecessary film may be stuck on an inner surface of the processing container 2 or on a surface of the showerhead 12. As described above, in the metal CVD method, it is difficult to deposit a film only on an upper surface of a wafer.
In addition, reaction products or by-products may be formed at a high-temperature portion, whose temperature is as high as the reaction temperature at a periphery of the stage 6, and on a wall surface of the processing container 2. On the contrary, at a low-temperature portion, a problem in which a non-reacted source gas condenses may be generated. Thus, in a conventional CVD method for W, WSi, TiN, Ti or the like, these unnecessary films and residual substances are decomposed and removed by introducing a cleaning gas such as ClF3 gas or NF3, gas, or a plasma into the processing container 2 every a predetermined number of wafers or every wafer. That is, an in-situ cleaning operation is carried out in general.
As described above, there are effective cleaning gases for removing unnecessary films of W, WSi, TiN, Ti or the like.
In the respect that a circuit element of a low resistance can be formed, aluminum and copper are superior. However, development for the method of filling a contact-hole or a groove for a circuit by means of CVD methods using organic aluminum or copper compound has just started. Thus, no effective cleaning gas has been found for aluminum films or copper films, yet.
That is, if a CVD process for copper is carried out by using an organic copper compound as a source material, there is a problem in which there is no etching gas that can etch residual substances of the copper compound within a sufficient short time, because the copper compound has only a low vapor pressure in general.
If a CVD process for aluminum is carried out by using an organic aluminum compound as a source material, there is a problem in which surfaces of the processing container, the showerhead and so on may greatly corrode if a cleaning gas for cleaning residual substances including aluminum is introduced, because the material of the processing container for the metal CVD method is aluminum in general.
This invention is intended to solve the above problems. The object of this invention is to provide a processing unit that can prevent a film-forming gas from flowing into a reverse side of a stage.
The invention is a film-forming unit comprising: a processing container in which a vacuum can be created; a stage arranged in the processing container, on which an object to be processed is placed; a process-gas supplying means for supplying a process gas into the processing container; a heating means for heating the object to be processed placed on the stage; a division wall that surrounds a lateral side and a lower side of the stage; an inert-gas supplying means for introducing an inert gas into a stage-side region surrounded by the division wall; and a gap-forming member whose inner peripheral portion is arranged above a peripheral portion of the object to be processed placed on the stage via a gap and whose outer peripheral portion is arranged above the division wall via a gap.
By supplying the inert gas into the stage-side region by means of the inert-gas supplying means, the inert gas can flow into the processing-space side through the inner-peripheral-side and outer-peripheral-side gaps that are formed by the gap-forming member.
Thus, it is prevented that the film-forming gas may reach the lateral side or the reverse side of the object to be processed. Thus, it is prevented that unnecessary films may be deposited on the lateral surface and the reverse surface thereof and on the surface of the stage.
Preferably, a contact portion for pressing and fixing the peripheral portion of the object to be processed is provided at a lower surface of the inner peripheral portion of the gap-forming member.
Preferably, the gap-forming member is vertically movable.
Preferably, a plurality of contact portions is provided at a predetermined height. In the case, even if the thickness of the object to be processed is variable because of a manufacturing tolerance or the like, the inert gas can be caused to flow into the processing-space side at a stable flow amount or flow speed.
Preferably, a height of the gap defined by the division wall and the outer peripheral portion of the gap-forming member is larger than a height of the gap defined by the peripheral portion of the object to be processed and the inner peripheral portion of the gap-forming member. For example, the height of the gap defined by the division wall and the outer peripheral portion of the gap-forming member may be about ten times as large as the height of the gap defined by the peripheral portion of the object to be processed and the inner peripheral portion of the gap-forming member.
In the case, even if a pressure change may happen in the supplied inert gas or the like, the pressure change may be easily absorbed, and the inert gas can be caused to flow always at stable flow amount and flow speed through the inner-peripheral-side gap.
Preferably, a temperature controlling means for setting a temperature of the processing container to be higher than a condensation temperature of the process gas and lower than a decomposition temperature and a reaction temperature of the process gas is provided for the processing container.
Preferably, a temperature controlling means for setting a temperature of the process-gas supplying means to be higher than a condensation temperature of the process gas and lower than a decomposition temperature and a reaction temperature of the process gas is provided for the process-gas supplying means.
Preferably, an electrostatic chuck is provided in the stage in order to fix the object to be processed placed on the stage.
Preferably, the gap-forming member is provided with a heater. In the case, the gap-forming member may be provided with a thermocouple.